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Saturday, 28 December 2013

Silent Crickets

Most people are aware that crickets produce sounds. We normally hear the "calling song", that is the sounds produced to attract females. Crickets can produce other sounds announcing territoriality or post-mating sounds. It has been shown that the calling songs are
highly species specific. That is females are “tuned” to answer the calls of
males of their own species. Singing by romantic males of other species just go
“over their heads”!

Females of some mole crickets, family Gryllotalpidae, can
produce songs, thereby answering calling males but females of the typical
crickets, family Gryllidae, are silent.

However, there are cricket species where neither sex produce any
sounds at all. How and why this happens in evolutionary terms is often debated.
Some of the ideas advanced include the obvious complexity of sounds in a particular kind of environment—perhaps, one with many cricket species or living in a odd place
where sounds are not needed or desired e. g.—caves, for example where hungry bats may
home in on a singing insect. In such a situation, males would be “selected” by
the predator and this would put the population at risk. Being quiet may have its advantages.

How do silent crickets find one another? Perhaps, they find each other using chemical or visual signals.

Here in my rainforest I have discovered some 53 species of
Gryllidae, give or take a few. Of this number some 35% are silent; they produce
no sounds at all. Is this absence of sound production associated with living in
the rainforest environment with the complexity of leaves, trees, shrubs, rocks
etc. Maybe leaves, shrubs etc reverberate and interfere with the calling
song. In such circumstances, maybe chemical signals get the sexes together. The
population numbers of rainforest crickets that don't sing seems higher than one observes elsewhere, so calling by song may not be as important as it is where
populations are dense. Cicada species seem to solve this problem by singing different times of the day and evening and singing during different seasons.

Here is a list of the non-singing species recorded at my site

F=Flightless, LW=long-winged,
capable of flight. A few species have both long-winged and short-winged (flightless)
morphs. Silvinella species live on the forest floor in leaf litter. Both sexes
are wingless. Most of the other are active on leaf surfaces at night. Euscyrtus lives in deep grasses and seems more active during the day.

Aphonoides australis (Walker) LW

A. lowanna Otte
& Alexander LW

A. weeronga
Otte & Alexanderor near LW

A. debilis
(Chopard) LW

A. sp nov. 1 LW

A. sp. nov. 2 LW

Genus nr Riatina (stridulatory file?) LW

Euscyrtus hemelytrus (Haan) F, LW

Umbulgaria hillimunga Otte & Alexander LW

Silvinella warraninna Otte & Alexander F

Amusurgus
noorundi Otte & Alexander F

A. hackeri
(Chopard) LW

A.
kanyakis Otte & Alexander LW

A. minmirri
Otte & Alexander LW

A. tinka Otte
& Alexander LW

Metioche
vittaticollis (Stål) F & LW

Trigonidium
bundilla Otte & Alexander F

Trigonidium ?australiana (Chopard) F

T. killawarra
or near Otte & Alexander F

Some
examples.

Gryllidae; Pteronemobiinae; Silvinella wirraninna female

Gryllidae; Trigonidiinae; Amusurgus mubboonis Otte and Alexander male

Gryllidae: Trigonidiinae; Amusurgus tinka female

Gryllidae; Trigonidiinae; Amusurgus hackeri (Chopard) female

Gryllidae; Trigonidiinae;Trigonidium bundilla male

Note the absence of a stridulatory file on the right wing on this and the other males below.

7 comments:

That is pretty fascinating. I thought there were silent crickets and katydids in Alberta, but it turned out they were just too high pitched for my old ears. But silent crickets in a rain forest is perplexing. In the understory, there should be little wind and chemical communication can't be very efficient over any distance.

Perhaps it has to do with predation. Are the singing crickets heavily parasitized/predated by villains using sound to locate their hosts?

Tremulation and drumming may also be involved. The latter may be particularly effective in species living among dry leaves on the forest floor. Some stoneflies, which live in a relatively very noisy environment by fast flowing streams, drum with their abdomens against rocks and logs. I will not be surprised if a similar behavior is found in crickets.

My brother has sent me a photo of a katydid or weta about 2cm long with short antennae and some spines on the back legs. Its legs have pale blue patches on a dark background and pale (possibly blue)triangular patches on a dark background on its body. It was digging antlion like holes in the sandy floor of a rock overhang on Erskine Ck in the Blue Mtns. Do you know what it is?

About Me

David and family moved to Kuranda, Queensland in 2002, following retirement from CSIRO Canberra, Australia. David, Barbara and an assortment of wildlife live in a rainforest setting. It is their first experience living in the tropics.
David's major interest is Entomology. He continues research in the Orthopteroid insects and is keenly interested in the biology of the rainforest.
This blog is a narrative of observations made in and around Kuranda.
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